1. Field of Invention
The present invention relates to a method and apparatus of CO—CO2 energy conversion cycle using solid oxide fuel cells (SOFC-CO2-ECC), in which CO2 is adopted as oxidant source for power generation. An innovative solution is provided, to solve greenhouse effect issue caused by increasing CO2 concentration in the atmosphere. Due to simultaneously high-temperature (700-1000° C.) catalytic and electrochemical reactions in the SOFC, CO2, a compound having extreme chemical stability, is cracked at about 800° C. following a chemical reaction below: CO2→CO(g)+½O2, to generate CO(g) and O2, then O2 electrochemically reacts with H2 (or other hydrocarbons, such as methane) in the SOFC for power generation. As such, CO2 may serve as a power source material in an overall reaction of the SOFC, and converted into a very useful energy source or compound CO, which can be derived into useful compounds or energy source, for example, aldehydes and alcohols, for regeneration of energy source, so as to complete an overall energy conversion carbon cycle of CO2→CO→derivatives of CO (fixation of CO2)→generation of energy source→CO2, and achieve zero emission of CO2. Technical solutions, auxiliary materials and equipments of the present invention are capable of effectively solving the problem of global extinction of organisms caused by greenhouse effect of CO2.
2. Related Art
The development of human civilization mainly relies on the development of the materials and technologies using energy sources. Among hydrocarbon oxides, coal and petroleum are extensively used due to the advantage of dual purposes of fixed position and mobility, and products after use of coal and petroleum are mainly oxides such as CO2 and H2O, or NOx, SOx, and COx, which are all air pollution gases except H2O. Furthermore, CO2 has high output and is a stable compound, and is only converted and consumed through plant photosynthesis, and thus being persistently remained in the atmosphere. Although CO2 may be prepared into dry ice and serve as gas for secondary enhancement of oil recovery for an oil well, it has few uses. Long-term high output of CO2 leads to sharp increase of CO2 level in the air, and triggers greenhouse effect, global warming, frequent natural disasters, and abnormal climate, and the problem has reached the degree of no time to delay. However, the “energy saving and carbon reduction policy” involves the use of nuclear energy and forest conservation and forestation, and also involves reduction of use of petroleum and coal fuels. However, the current civilization improvement and economic development have to rely on supply of energy sources. In addition to compromise of the two aspects, it is necessary to find a new solution of CO2 problem.
Due to international extensive consumption and use of fossil energy sources, the amount of the product CO2 is continuously increased, and the whole atmosphere of the earth is polluted, and thus resulting in greenhouse effect and threats and risks to living conditions of human being and other related organism on the earth. It is estimated that CO2 content in the atmosphere is continuously exponentially increased to 380 ppm in 2000, and the annual increase rate is gradually accelerated, which may be attributed to man's increasing combustion of fossil fuels. Therefore, the issue of “energy saving and carbon reduction” is raised, to rescue the earth and solve the problem of human survival. In this issue, various processes are set forth to provide a solution for the CO2 problems. It is emphasized in Copenhagen conference (COP-15) that in order to combat global climate change, global carbon emission must be reduced greatly, to control the global temperature rise to be below 2° C. and the global average CO2 concentration in 2050 to be returned to 450 ppm, because among greenhouse gases (water vapor=36-70%; carbon dioxide=9-26%; methane=9%; ozone=3-7%), CO2 is the main cause.
At present, solution of this issue in world is directed to development of the technologies of CO2 capture, storage and, reutilization. It is expected to effectively lower CO2 content in the atmosphere and solve the greenhouse issue through fixed storage or by fixing CO2 through a chemical reaction, such as CO2+CaO, to generate a solid such as CaCO3, so as to extract large volume of CO2(g) from the atmosphere for solidification.
For the CO2 cracking chemical reaction CO2(g)→CO(g)+½O2(g), a spontaneous reaction temperature is 3001.5° C. according to thermodynamic calculation, and thus the reaction cannot be effectively overcome and implemented by using the current useful technology and apparatus. Therefore, CO2 greenhouse gas cannot be solved, and becoming a problem around the world.
SOFCs have advantages of high energy conversion efficiency, low noise, low environment pollution, high reliability, and diversity of fuel, and have the potential of challenging “internal-combustion engine”, and thus being capable of solving the problem of energy shortage in future. Especially, the fossil energy sources are gradually depleted, and replaced by gasified and liquefied coal sources, and thus coal fuel era comes, in which SOFCs are the apparatus of main energy source converter and will play an innovative role in the era. With the successful of performance stability and long-term operation test of SOFCs, technology and functions of apparatus become mature gradually. In the future, distributed or centralized power generators or power plants will gradually replace the existing coal-fired power plants, and thus the economic benefits are very large.
Presently, in an SOFC, H2, natural gas, or a fossil fuel (for example, hydrocarbons such as methane, alcohols, alkanes or alkynes, or even diesel) is fed into an anode as fuel, and O2 in air is fed into a cathode as oxidant, and the chemical energy is directly converted into electric energy via simultaneously or sequentially electrochemical and catalytic chemical reactions. Main products at the anode are CO2 and H2O, and O2 depleted air at the cathode. Therefore, main cause CO2 of greenhouse effect is naturally generated. However, as the energy source conversion rate (up to 70-80%) of the SOFC is much higher than that of a conventional coal-fired power plant (generally about 20-30%), for a certain amount of fuel, the SOFC can achieve a function of energy increase and carbon reduction. This advantage can only lower the emission of CO2, and thus partly achieving the purpose of energy saving and carbon reduction.
At present, solving of the problem of greenhouse effect in world is directed to development of technologies of CO2 capture, storage, and reutilization. However, the development is still at an initial stage, and no specific and effective method is set forth for solving the problem. One process or procedure is provided, in which CO2 is fixed and stored, or converted into a solid through a chemical reaction, such as CO2+CaO→CaCO3, so as to extract large volume of CO2(g) from the atmosphere for solidification, thereby effectively lowering the CO2 content in the atmosphere. Furthermore, a primitive process in the nature is to plant a lot of forests and seaweed plants, such that chlorophyll photo-synthesis is performed, to convert CO2 into plant ingredients, thereby lowering the CO2 content in the atmosphere. Both the processes are feasible but contradict the increase tendency in energy source demand, have many difficulties, are passive solutions and actions, and belong to natural carbon cycle.
According to the method and apparatus for energy conversion cycle based on SOFC and utilizing CO2 source of the present invention, waste CO2, main cause of greenhouse effect, is converted into energy source materials by an SOFC, by cracking CO2 as SOFC cathode oxidant, in presence of SOFC anode fuel such as H2 following CO2→CO(g)+½O2, CO is generated for power generation. CO is a high-activity compound, and may be used as fuel of the SOFC (in SOFC anode) for power generation with O2 in air at the cathode, to generate electric energy and CO2, thereby “use-regeneration” and power generation ECC of CO2 is completed. Furthermore, CO may react with H2 and O2 to synthesize a stable compound, such as useful solid or liquid compounds of alcohols, aldehydes, and acids, and thus being safely stored in the earth for recycle and reutilization. As a result, the CO2 content in the atmosphere is lowered, and the problem of greenhouse effect is solved. The process and the apparatus of the present invention are an active process for solving the CO2 problem.